Radio Frequency Identification (RFID) applications are proliferating as the economies of automated tracking and identification are being realized by the global community. RFID is the ability to detect, read, and/or write data to tags that are affixed to “things.” Cost of the RFID tag is the predominant parameter dictating applicability of this technology.
There are several categories of RFID tags and readers in use and proposed. The technology currently is predominantly passive. Passive implies that the tags have no battery. They derive power from a reader that transmits electromagnetic energy to the tag, which in turn reflects or modulates the energy signal back to the reader. While passive tags and readers are relatively inexpensive, they have severe limitations dictated by physics. For example, passive tags and readers have a limited range (from 0.1 cm to 6 meters) and are non-operational when blocked or shielded by metal objects, liquids and certain solid materials. In such systems, data rates are limited to approximate 6 mph “drive-thru” speeds thru portals, conveyors, etc. Further, passive systems have limited data storage capacity and no sensing capability.
There are also “active” tags that derive their power from incorporated batteries. Such devices add significant value to the process of inventory tracking and In Transit Visibility (ITV) enabling processes such as Total Asset Visibility (TAV). Relative to passive tags, active tags have a greater data acquisition range (0 to 100 meters). Active tags have the ability to provide Real Time Location System (RTLS) effectivity, to automatically provide theft deterrence thru continuous and automatic “presence detecting,” and to enable tracking through processes such as manufacturing, shipping, on trucks, forklift transfer, and warehousing. A disadvantage of active tags is that they cost more than passive tags and this requires that these tags achieve maximum performance, add value to supply chain management and achieve these goals with absolute lowest cost.
Many active tags simply “beacon” or periodically transmit data. However, this approach has limitations. In certain instances, the continuous battery consumption is prohibitive since RF data transfer is only required when handling or processing the tagged items. In addition, it is often desired to associate a specific tagged item with a process such that the tagged item can be associated with a specific event, time or operator and beacon tags do not provide this utility. It is often desired to locate a specific tagged item in a situation where many identical items are tagged. It may be desired to be able to change the tag's mode of operation, i.e. turn the beacon mode “off or on”, or change the beaconing rate. A specific tag should be able to respond under any of these circumstances. The ability to transfer data from the tag via a medium other than RF signals is also a desirable functionality since many locales and operations (such as aircraft flight) require RF silence.
Therefore, current commercial tags offer secondary triggering or communication modes of operation. “Triggering” is the remotely transmitted command to a tag directing that it execute a function such as “transmit RF, store data, or take a sensor reading”. These secondary modes are restricted to the use of magnetic or RF fields to effect the triggering or communication. RF and magnetic triggered tags have the problem of being non-discriminatory, that is, the nature of RF fields is that they cannot be restrained to a narrow effective Field of View (FOV) and hence are not tag specific in the presence of many tags. They are also costly.
Low frequencies (magnetic domain) such as 125-134 KHz require very close proximity to actuate the tag response and often will not work with the tag attached to ferrous objects. Higher frequencies such as 915 MHz also are affected by metal items and are often reflected making single tag actuation less reliable than is required. All of these triggering mechanisms are large, bulky, and expensive. Handheld triggers or communicators are also large and bulky. Many applications require that the tags and readers comply with Intrinsic Safety requirements. This task is significantly complicated and more costly with low frequency devices due to the necessity for relatively high source power. Additionally, the transfer of data is at relatively low speeds.